Damage Tolerance of a Sandwich Panel Containing a Cracked Square Lattice Core

The fracture response of a sandwich panel, with a center-cracked core made from an elastic-brittle square lattice, is explored by finite element simulations and simple analytical models. First, predictions are given for the unnotched strength of the sandwiched core and for the fracture toughness of the lattice under remote tension, remote compression, or remote shear. It is assumed that the lattice fails when the local stress in the cell wall attains the tensile or compressive strength of the solid, or when local buckling occurs. Failure maps are then constructed for a cracked sandwich panel, with axes given by a dimensionless crack length and dimensionless height of the sandwich core. The shear strength of the cracked sandwich panel is examined in detail. The precise form of the failure map for shear loading depends upon the tensile failure strain of the solid and upon the relative density of the lattice. The relevance of the shear failure map to lattices made from a wide range of engineering materials is illustrated through material-property charts. An extension of the method to cyclic loading is discussed.